1. Field of the Invention
This invention relates to charge transfer devices, and more particularly, to a floating clock electrode sensor affording non-destructive signal sensing from a charge transfer device.
2. State of the Prior Art
Charge transfer devices (CTD) including charge coupled devices (CCD) are known in the prior art. In general, charge packets propagate down a CCD channel and at some suitable point are sensed. Sensing may be performed either in a destructive or a non-destructive manner. Since the present invention relates to non-destructive sensing, consideration of only non-destructive prior art sensing techniques is herein set forth.
One technique, typically employed for destructive sensing, is to provide a diffused sensing region at the point of readout from the CCD channel. In some versions, diffused sensing regions have been provided which attempt to afford non-destructive readout. This technique is basically ineffective since there is charge retention on the diffused sensing node which, expressed in terms of inefficient transfer of signal charge from the diffused region, gives rise to considerable signal dispersion.
An isolated floating gate electrode technique has also been employed heretofore in the prior art. Known techniques, however, provide that the gate electrode employed for sensing remain in a floating condition at all times. This has several disadvantages, a principal one being that there is inadequate control over the potential of the isolated floating gate sensor electrode and hence inadequate control of the surface potential in the CCD channel underlying that sensor electrode. Elaborate and complex circuit provisions are required to compensate for this condition, themselves introducing diverse other problems. Non-destructive split-clock-type sensing used in conjunction with preweighted summation over all readouts (tap-points) of a CTD requires gated integration of clock line currents and does not permit independent buffered access to each tap-point.